1. Field of the Invention
The subject of this invention is air bleed on a pivoting blade of a turbomachine stator.
2. Discussion of Background
A large number of turbomachines include stator blades with a pivoting assembly so as to modify the gas guiding characteristics depending on the speed of the machine. Specialists say that the blade setting is variable. The blade setting is varied by a throttle control surrounding the stator and usually including an actuation ring to which connecting rods are articulated, the opposite ends of the connecting rods engaging with extreme portions of pivots of blades that extend outside the stator. Rotation of the ring around the stator tilts the connecting rods and pivots the blades about the pivot axis.
It is also known that gases can be taken in on the surface of the blades. Such an arrangement is normally applied to compressor blades to suck in the boundary layer and consequently increase the compression ratio. Intake takes place through hollow channels formed in the blades and opening up on their surface, and air is recovered and reinjected into another portion of the machine. Although this process has been known for several decades, it has been suggested particularly for fixed setting blades that can be used to build intake ducts that are also fixed. This description discloses satisfactory solutions to the seal problem that arises when an intake system is applied to variable setting blades, necessarily adjusted with a clearance through the stator case.
However, we will mention document U.S. Pat. No. 5,795,128 in which pivoting blades are provided with an air intake system including a header pipe covering the outside ends of the pivots and in which the hollow intake drillings drilled at the centre of the pivots open up. This design imposes a header pipe applied to the stator at the blades, which is a design constraint that cannot always be respected. One disadvantage of this design is due to the control rods that pass through the header pipe and require a particular sealing means.
Document FR-A-2 433 106 discloses a similar system except that the header pipe is made in the case in front of the central portions of the blade pivots. The hindrance associated with interference between the control rods and the header pipe disappears, but layout constraints are even greater. The airflow is affected by sudden direction and section variations that induce large head losses.
Document U.S. Pat. No. 5,472,314 describes a system in which the blade includes a pivoting part at the leading edge, a fixed part at the trailing edge, and an intermediate flexible part; air passes through the fixed part and the flexible part between the outside of the case and the pivoting part. This innovative design is expensive and complicated.